This invention relates to an internal combustion reciprocating engine having an intake gas conduit system which improves the charging of the cylinders by utilizing oscillations of the gases.
The output or the mean effective pressure of internal combustion reciprocating engines are fundamentally affected by the quantity of the charge introduced into the engine cylinders. In Otto-engines the charge is, during the suction cycle, introduced into each engine cylinder through the intake opening thereof as intake gas formed of an air-fuel mixture. In diesel engines, the intake gas entering the cylinder during its suction cycle generally contains no fuel, or has only such a small fuel quantity that the resulting air-fuel mixture ratio is insufficient for self-ignition. The still missing fuel proportion or the entire fuel quantity is added into the cylinder to the intake gas at the end of the compression cycle, whereby the combustion charge is formed. For this reason by "intake gas" entering the cylinder through its intake opening there is meant here--dependent upon the system and mode of operation of the engine--either air or an air-fuel mixture.
For the purpose of increasing the mean effective pressure of an internal combustion engine, methods are known according to which oscillations appearing in the intake gas conduit system coupled to the intake openings of the engine cylinders are utilized for increasing (intensifying) the combustion charge of the cylinders. The intake gas oscillations generated by the discontinuous suction effect of the engine cylinders may be particularly advantageously utilized in intake gas conduit systems in which at the most four engine cylinders--whose suction cycles do not significantly overlap one another--are connected with a common resonator vessel which communicates with at least one resonance tube. The oscillating system composed of the resonator vessel and the resonance tube has a certain natural frequency. If the natural frequency of the system at least approximately corresponds to the frequency of the discontinuous, periodical suction effected by the cylinders, the gas oscillations generated by this periodical suction are amplified to a substantial extent and are utilized for increasing the charge for the cylinders.
The internal combustion engines, however, do not, as a general rule, draw the air required for the intake gas directly from the surrounding atmosphere; rather, to the intake gas conduit there is coupled an air filter and, in some instances, there is also attached a particular charging device. In such cases between the resonance tube and the filter element of the air filter or between the resonance tube and the charging device an arrangement has to be installed which defines a volume serving for the dampening of the oscillations of the combustion gas. The purpose is, in part, to ensure that the choking effect of the mentioned devices does not adversely affect the gas oscillations generated in the oscillating system and, in part, to ensure that the gas oscillations do not adversely affect the proper operation of the charging device or the air filter. Intake gas conduit systems of these types are disclosed, for example, in Hungarian Pat. No. 161,323 and U.S. Pat. No. 3,796,048. In these known arrangements the first, second and third cylinders of a six-cylinder series engine on the one hand and its fourth, fifth and sixth cylinders on the other hand, form two cylinder groups. The suction cycles of the individual cylinders forming one and the same group do not overlap. The intake openings of the cylinders belonging to one and the same group are coupled with a common resonator vessel and to each resonator vessel there is coupled a resonance tube. The resonance tubes are connected with one another by means of a common dampening vessel. The intake gas inlet opening of the dampening vessel communicates with the pressure side of the charging device by means of a coupling conduit.
By virtue of the usual firing sequence of 1-5-3-6-2-4 of six-cylinder engines and the usual firing intervals, the suction cycles within each cylinder group are 240.degree. apart (expressed as the angle of rotation of the engine crank shaft). At the same time the suction cycles of the two cylinder groups are offset by 120.degree., that is, by exactly one-half phase. This means that likewise, the intake gas oscillations generated in the oscillating systems of the separate cylinder groups are shifted one-half phase with respect to one another. Thus, when in the resonator vessel of the one cylinder group there prevails the maximum of the pressure oscillation, in the other group, at the same time, a pressure minimum will prevail. The situation is similar at the inlet openings of the resonance tubes at the dampening vessel: when at the inlet opening of the one resonance tube associated with the one cylinder group there prevails the maximum intake gas velocity in the direction of the cylinder group, then at the inlet opening of the resonance tube belonging to the other cylinder group a maximum but oppositely oriented intake gas velocity prevails (that is, the last-named velocity is oriented towards the dampening vessel). The non-steady mass flows caused by the intake gas oscillations therefore equalize one another at the dampening vessel. At the intake gas inlet opening of the dampening vessel there is thus obtained a steady intake gas velocity which corresponds to the intake gas consumption of the engine and in the dampening vessel a steady pressure level prevails. This steady pressure level provides the necessary boundary conditions for the intake gas oscillations appearing in the oscillating system, whereas the steady mass flow which is set at the intake gas inlet opening of the dampening vessel ensures a steady operation and good efficiency of the turbocharger. For achieving the above-described equalization and oscillation dampening, a very small dampening volume is sufficient, because the size of the volume does not play a significant role in the equalization. The structural advantages derived from this circumstance are apparent: no difficulties will be encountered in installing a dampening vessel of small volume at the engine.
The situation is fundamentally different in engines where each cylinder group has its own, separate dampening vessel; that is, to one dampening vessel there is connected only a single resonance tube serving one cylinder group. Such internal combustion engines are one, two, three and four-cylinder engines and also multi-cylinder engines in which, for constructional reasons, the coupling of more than one resonance tube to the dampening vessel is not possible or is impractical. In such engines, because of the intake gas oscillations generated in the resonator vessel and the resonance tube associated with the respective cylinder group (that is, oscillations generated in the oscillating system) a non-steady suction, that is, a pulsating mass flow appears in the dampening vessel associated with the respective cylinder group. In order to ensure that despite such a non-steady suction a relatively steady pressure level is set in the dampening vessel and further, a relatively steady intake gas velocity is set at the intake gas inlet opening of the dampening vessel, the volume of the dampening vessel has to be very large: it has to be thirty to fifty-fold the total swept volume of the engine and therefore could amount to as much as 100 liters. Consequently, it is very difficult to accommodate such large dampening vessels and thus, in engines of the last-discussed type intake gas conduit systems enhancing cylinder charging by intake gas oscillations as described above could not be used.